The present invention relates to a device and a method for positioning a rotatable cylinder of a printing press.
An offset printing press has a plurality of rotatable cylinders including plate cylinders and blanket cylinders. Each of the plate and blanket cylinders carries a printing cover, which are a printing plate and a printing blanket, respectively. Each printing plate and printing blanket is wrapped around the respective cylinder. The ends of each printing plate and printing blanket are affixed to the respective cylinder.
Each printing plate has an image to be printed. The image is transferred from the printing plate to the associated printing blanket as the printing plate and the printing blanket are rotated against each other. The image is transferred to the material being printed, such as a web of paper, from the printing blanket as the web is moved past the rotating printing blanket.
In order to change the printing, the printing plate is replaced. Also, the printing blanket must periodically be replaced due to wear. Due to the construction of the printing press, only a limited work area is present to complete the replacement of the printing plate and/or the printing blanket. During a replacement operation of the printing plate and/or the printing blanket, the cylinders are rotatably driven to locate the cylinders in an access or index position for access to the ends of the printing plate and/or the printing blanket. In order to rotate the cylinders to the access position, the cylinders are driven by the same motor which drives the cylinders during the printing operation. If the cylinders are driven at a relatively high rate of speed, the cylinders may overrun the access position due to rotational inertia. If the cylinders are driven at a relatively low rate of speed, excessive time is wasted.